159 research outputs found
The effect of male coloration on female mate choice in closely related Lake Victoria cichlids (Haplochromis nyererei complex)
No full textWe studied the effect of male coloration on interspeciÆc female mate choice in two closely related species of haplochromine cichlids from Lake Victoria. The species differ primarily in male coloration. Males of one species are red, those of the other are blue. We recorded the behavioral responses of females to males of both species in paired male trials under white light and under monochromatic light, under which the interspecific differences in coloration were masked. Females of both species exhibited species-assortative mate choice when colour differences were visible, but chose non-assortatively when colour differences were masked by light conditions. Neither male behaviour nor overall female response frequencies differed between light treatments. That female preferences could be altered by manipulating the perceived colour pattern implies that the colour itself is used in interspecific mate choice, rather than other characters. Hence, male coloration in haplochromine cichlids does underlie sexual selection by direct mate choice, involving the capacity for individual assessment of potential mates by the female. Females of both species responded more frequently to blue males under monochromatic light. Blue males were larger and displayed more than red males. This implies a hierarchy of choice criteria. Females may use male display rates, size, or both when colour is unavailable. Where available, colour has gained dominance over other criteria. This may explain rapid speciation by sexual selection on male coloration, as proposed in a recent mathematical
model
Mechanisms of rapid sympatric speciation by sex reversal and sexual selection in cichlid fish
No full textMechanisms of speciation in cichlid fish were investigated by analyzing population genetic models of sexual selection on sex-determining genes associated with color polymorphisms. The models are based on a combination of laboratory experiments and field observations on the ecology, male and female mating behavior, and inheritance
of sex-determination and color polymorphisms. The models explain why sex-reversal genes that change males into females tend to be X-linked and associated with novel colors, using the hypothesis of restricted recombination on the sex chromosomes, as suggested by previous theory on the evolution of recombination. The models reveal
multiple pathways for rapid sympatric speciation through the origin of novel color morphs with strong assortative mating that incorporate both sex-reversal and suppressor genes. Despite the lack of geographic isolation or ecological differentiation, the new species coexists with the ancestral species either temporarily or indefinitely. These
results may help to explain different patterns and rates of speciation among groups of cichlids, in particular the explosive diversification of rock-dwelling haplochromine cichlids
Rapid Establishment of a Regular Distribution of Adult Tropical Drosophila Parasitoids in a Multi-Patch Environment by Patch Defence Behaviour.
No full textFemales of the larval parasitoid of Drosophila, Asobara citri, from sub-Saharan Africa, defend patches with hosts by fighting and chasing conspecific females upon encounter. Females of the closely related, palearctic species Asobara tabida do not defend patches and often search simultaneously in the same patch. The effect of patch defence by A. citri females on their distribution in a multi-patch environment was investigated, and their distributions were compared with those of A. tabida. For both species 20 females were released from two release-points in replicate experiments. Females of A. citri quickly reached a regular distribution across 16 patches, with a small variance/mean ratio per patch. Conversely, A. tabida females initially showed a clumped distribution, and after gradual dispersion, a more Poisson-like distribution across patches resulted (variance/mean ratio was closer to 1 and higher than for A. citri). The dispersion of A. tabida was most probably an effect of exploitation: these parasitoids increasingly made shorter visits to already exploited patches. We briefly discuss hypotheses on the adaptive significance of patch defence behaviour or its absence in the light of differences in the natural history of both parasitoid species, notably the spatial distribution of their hosts
A test of fitness consequences of hybridization in sibling species of Lake Victoria cichlid fish
No full textInternational audienceSeveral hundred species of haplochromine cichlid fish have evolved rapidly in Lake Victoria. Divergent sexual and ecological selection probably played an important role in this radiation, generating divergent mating preferences and preference-trait covariance. However, the segregation of hybrid inviability or infertility genes could also potentially generate preference-trait covariance, and the mechanisms that cause the evolution of divergent mating preferences have not been investigated in detail in any cichlid species pair. We investigated intrinsic fitness of hybrids between two sister species in the genus Pundamilia, one of the most species-rich genera of Lake Victoria cichlids. Fitness-related traits were measured in nonhybrid offspring of both species, and in the first and second hybrid generations. There were no differences in fecundity, fertility, sex ratio or growth rates either between the sister species or between these and their hybrids. By contrast, there was a difference in offspring survival between the two sister species. Offspring survival was dependent only on the species of the mother, regardless of whether the cross was conspecific or heterospecific. Further, eggs tended to be larger in the hybrids than in one of the parental species. Hence, hybrids suffered no intrinsic fitness reduction relative to nonhybrids. Our data suggest that intrinsic hybrid incompatibilities are unlikely to have caused speciation in Pundamilia, nor to maintain species boundaries in this system
Invasion and fixation of sex-reversal genes
No full textWe simulated a meta-population with random dispersal among demes but local mating within demes to investigate conditions under which a dominant female-determining gene W, with no individual selection advantage, can invade and become fixed in females, changing the population from male to female heterogamety. Starting with one mutant W in a single deme, the interaction of sex ratio selection and random genetic drift causes W to be fixed among females more often than a comparable neutral mutation with no influence on sex determination, even when YY males have slightly reduced viability. Meta-population structure and interdeme selection can also favour the fixation of W. The reverse transition from female to male heterogamety can also occur with higher probability than for a comparable neutral mutation. These results help to explain the involvement of sex-determining genes in the evolution of sex chromosomes and in sexual selection and speciation
Parasite-mediated sexual selection and species divergence in Lake Victoria cichlid fish
No full textInternational audienceWe investigate the role of parasite-mediated sexual selection in the divergence of two species of Lake Victoria cichlids. Pundamilia pundamilia and Pundamilia nyererei represent a common pattern of male nuptial colour divergence between haplochromine sister species: metallic grey–blue in P. pundamilia and bright yellow and red in P. nyererei. Female mating preferences for different male colours maintain the genetic and phenotypic differentiation of the two species in clear water. Previous work indicated that the red coloration of P. nyererei males, which is subject to directional sexual selection, may be a carotenoid-dependent signal of parasite infestation rate. In the present study, we find a parallel result for P. pundamilia: bright blue males are infected with fewer species of parasites. We also find that parasite infestation rates differ quantitatively between the two species in a way that is consistent with species differences in diet and microhabitat. We conclude that parasite-mediated sexual selection may have contributed to the divergence of female mating preferences between P. pundamilia and P. nyererei, and may currently strengthen reproductive isolation between these species
Kennis voor Deltabeslissingen: Grootse plannen voor waterveiligheid
No full textEr is een toenemende internationale belangstelling voor de ‘Deltabenadering’. Regelmatig presenteren deskundigen en beleidsmakers aan buitenlanders Nederlandse kennis van waterveiligheid en kunde in het maken van grote waterveiligheidsplannen. In dit artikel besteden we bijzondere aandacht aan het managen van die kennis ten behoeve van het maken van die plannen, in dit geval het Deltaprogramma; hoe ziet dat facet van de Deltabenadering er eigenlijk uit?Multi Actor SystemsTechnology, Policy and Managemen
Kennis voor Deltabeslissingen. Grootse plannen voor waterveiligheid
No full textEr is een toenemende internationale belangstelling voor de ‘Deltabenadering’. Regelmatig presenteren deskundigen en beleidsmakers aan buitenlanders Nederlandse kennis van waterveiligheid en kunde in het maken van grote waterveiligheidsplannen. In dit artikel besteden we bijzondere aandacht aan het managen van die kennis ten behoeve van het maken van die plannen, in dit geval het Deltaprogramma; hoe ziet dat facet van de Deltabenadering er eigenlijk uit?Multi Actor SystemsTechnology, Policy and Managemen
Cichlid Fish Diversity Threatened by Eutrophication That Curbs Sexual Selection
No full textCichlid fish species of Lake Victoria can interbreed without loss of fertility but are sexually
isolated by mate choice. Mate choice is determined on the basis of coloration, and strong
assortative mating can quickly lead to sexual isolation of color morphs. Dull fish col-
oration, few color morphs, and low species diversity are found in areas that have become
turbid as a result of recent eutrophication. By constraining color vision, turbidity interferes
with mate choice, relaxes sexual selection, and blocks the mechanism of reproductive
isolation. In this way, human activities that increase turbidity destroy both the mechanism
of diversification and that which maintains diversity
Female mating preference functions predict sexual selection against hybrids between sibling species of cichlid fish
No full textInternational audienceThe evolutionary outcome of interspecific hybridization, i.e. collapse of species into a hybrid swarm, persistence or even divergence with reinforcement, depends on the balance between gene flow and selection against hybrids. If female mating preferences are open-ended but sign-inversed between species, they can theoretically be a source of such selection. Cichlid fish in African lakes have sustained high rates of speciation despite evidence for widespread hybridization, and sexual selection by female choice has been proposed as important in the origin and maintenance of species boundaries. However, it had never been tested whether hybridizing species have open-ended preference rules. Here we report the first experimental test using Pundamilia pundamilia, Pundamilia nyererei and their hybrids in three-way choice experiments. Hybrid males are phenotypically intermediate. Wild-caught females of both species have strong preferences for conspecific over heterospecific males. Their responses to F1 hybrid males are intermediate, but more similar to responses to conspecifics in one species and more similar to responses to heterospecifics in the other. We suggest that their mate choice mechanism may predispose haplochromine cichlids to maintain and perhaps undergo phenotypic diversification despite hybridization, and that species differences in female preference functions may predict the potential for adaptive trait transfer between hybridizing species
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